Method of dissolving asphaltene deposits



METHOD OF DISSOLVING ASPHALTENE DEPOSITS Abraham Shapiro, Pasadena, Calif., assignor to Socony Mobil Oil Company, Inc., New ration of New York York, N.Y., a corpo- T his invention relates to solvents for asphaltenes and heterogeneous solid deposits which include asphaltenes.

The term asphaltenes is applied to those components of petroleum which are dark-colored, amorphous, neutral with respect to acids and alkalies, insoluble in light paraflinic hydrocarbons (specifically, petroleum ether), and soluble in benzene, chloroform, or carbon disulfide. They are polycyclic aromatic compounds of very hgh molecular weight containing not only carbon and hydro gen but also oxygen or sulfur or both and, in some cases, a substantial proportion of nitrogen, 'At ordinary temperatures such 'solutionsas they form are collo'dal. At higher temperatures, for example 120 C., the molecular weights are much decreased and the asphaltenes are capable of formingtrue solutions. f

When asphaltenes occur in petroleum, they may be colloidally dissolved or may be in the form. of suspended solid particles. Under some conditions the suspended particles adhere to oil-well tubing, pipe lines, etc., and

'the colloidal asphaltenes are subject to deposition by electrical effects created by motion of the petroleum and by ground currents. In gas wells, deposits of bituminous material including large proportions of asphaltenes are sometimes formed by evaporation of the hydrocarbon liquids collecting in the bottoms of the wells. The deposits formed in these ways often include other sol'ds such States Paten I and various narrow petroleum fractions of differen'tvdeof the ketone are good solvents for asphaltenes, sulfi-" ciently effective to be used for the removal of asphaltene grees of volatility and saturation which are prepared for use as solvents and designated by trade names.

withinthe range of about five to forty percent by volume deposits from pipe lines and the like.

In the case of aromatic hydrocarbon liquids, which have fairly; good solvent power for asphaltenes without addition of a ketone, the simple visual technique is not satisfactory. I-have-testedmixtures of such liquids with to the other tube. The two tubes are whirled in a centri fuge for about fifteen minutes, and then the amount of precipitated asphaltene in each tube is observed. p

In all cases, I have found that addition of acetone and similar ketones to aromatic hydrocarbon liquids causes a remarkable, increase in solvent power for asphaltenes.

mixtures for use in the oil fields.

of normally liquid hydrocarbons of low viscosity, it is I have not investigated the normally gaseoushydrocarbons, such as butane, nor the viscous hydrocarbon liquids, such as lubricating oil, because such substances are obviously not practical as. components of solvent But within the class apparent that addition of an aliphatic ketone, up to at least C always increases solvent powerfor asphaltenes, whether the hydrocarbon be paraffinic, olefinic, naphthenic, or aromatic, and whether the unassisted hydro-- carbon be capable of dissolving asphaltenes or not.

For use upon deposits which consist predominantly of asphaltenes or of mixtures of asphaltenes with insoluble as sand, clay, and wax, with the asphaltenes acting as the principal cementing material. Such deposits are hard, extremely tenacious, and'most difficult to removevby scraping, washing, or any other method which has been employed heretofore.

Numerous solvents for asphaltenes are known in the cracked petroleum distillates are so slow in their action 1 and have so little capacity-for asphaltenes; that their use requires excessive amountsof time and material.

I have discovered that mixtures of hydrocarbon l'quds with acetone or a similar ketone are good solvents for asphaltenes and are fully suitable for cleaning hard black 5 1 deposits from oil wells, gas wells,-and pipelines. This is unexpected, because the ketones themselves are very poor solvents for asphaltenes and were not known to have any property which would result in creation of solvent power for asphaltenes in their mixtures. i s v t" In the case of colorless hydrocarbon liquids of paraffinic, olefinic, or naphthenic nature, which dissolve asphaltenes to a negligible degree or not at all, I have tested ketone mixtures by placing a small lump of asphaltene material in a test tube, adding some of the mxture to be tested, shaking the tube, and observing the degree and rapidity of darkening of the liquid by dissolved asphaltenes.

In this manner I have examined numerous mixtures of acetone, 2,4-pentanedione, and' diacetone alcohol with gasoline, kerosene, A.S.T.M. naphtha, rubber solvent,

matter such as sand and clay, I pre er to employ a mixture of acetone and an aromatic hydrocarbon liquid such as Edeleanu extract from petroleum distillates, and it is in some cases desirable to add a hydroxy-aromatic material such as cresylic acid, which acts as a softening agent and thus facilitates the attack of the solvent mixture upon extremely hard deposits. 5 1

The Edeleanu extract I have employed has the follow ing properties: 1

Gravity A.P.I 26.0 A.S.T.M.- distillation: Initial F'... 340 a 10% ,",F 373 50% 3F; ,425 ;L F; 487 Endpoint; VF; 520 Olefines and aromatics percent 75-82 Bromine'number f 4-8 The maximum solvent power of mixtures of thi s liquid with acetone-occurs at 65,% by volume of the Edeleanu extract and about .35 acetone. This mixture was. tested asfollows:

Five grams of dehydrated asphaltene was dissolved in 130 cc. of Edeleanu extract by heating to about 300 F. The resulting suspension was divided equally and placed in two graduated centrifuge tubes. Enough acetone was added to one tube to bring the level up to cc., and enough Edeleanu extract was'added to the other to bring the contents to the same level. The tubes were then thoroughly shaken and placed in a centrifuge for fifteen minutes. When the tubes were examined, it was found that about 2 cc. of dark precipitate had settled out in the ti ed use,

In each' case, I have found that ketone-hydrocarbon mixtures Proportion Proportion Edeleanu Acetone, Temperature Extract, Percent Drp,F Percent For use upon deposits which contain substantial proportions of wax in addition to the asphaltenes and inorganic material, it is preferable to use a predominantly paraffinic hydrocarbon liquid of moderately low average molecular weight, such as gasoline.

It is often desirable to employ mixtures which include much less of the ketone than that required .to yield the maximum solvent power for asphaltenes. In some cases the reason is merely economic, depending on the fact that a mixture containing relatively little ketone may yield adequate results at lower cost. But in other cases the usefulness of the composition is involved, as when it is preferred that the solvent power of the hydrocarbon for wax not be diminished by the addition of too much ketone.

A number of solvent compositions consisting of or including mixtures of hydrocarbons with acetone have been successfully employed in the field. The following two have been found to be fully satisfactory and are now in regular use in California oil and gas fields.

Composition A: Percent by volume except asphaltenes. For example, in the case of an 11,000-foot gas well which was almost completely clogged with such a deposit, the well-was shut down in the late afternoon and about a barrel of composition A was injected. The well remained shut down overnight, and it was reopened at about nine oclock the next morning and permitted to blow itself out with its own pressure. The well was then able to produce gas at its full capacity, and subsequent testing with a feeler showed no indication of any remaining deposit. The previous time the same well had become clogged there had been a completely unsuccessful attempt to dissolve the deposit with Edeleanu extract, and it was necessary to remove the deposit by drilling. Composition A has been used numerous times in similar wells, with dosages of from half a barrel to a barrel.

Composition B" is chosen for dissolving deposits, common in lead lines and other piping, which include considerable amounts of wax together with asphaltenes and inorganic matter. These deposits are softer and usually more accessible, and yet they have presented a serious problem because heretofore the wax and the asphaltenes have not been subject to the same solvents or mixtures of solvents, and each has tended to protect the other from the solvents which might have been effective.

The present application is a continuation-in-part of my copending application Serial No. 356,608, filed May 21, 1953, now abandoned.

I claim as my invention:

'1. A process of removing from oil and gas wells and from petroleum pipe lines deposits which include asphaltenes and which are substantially devoid of readily petroleum-soluble materials, comprising: exposing said deposits to the solvent action of a mixture including a Edeleanu extract 55 Acetone l0 Cresylic acid 35 Composition B:

Unleaded aviation gasoline 67 The Edeleanu extract is derived from a'kerosene dstill'ate and is essentially the same material as that described above, with some slight variations in the gravity and distillation range. The aviation gasoline -has the following Composition A" is chosen for dissolving the hard, coke-like deposits which contain little organic material liquid-sulfur-dioxide extract from a petroleum distillate and acetone, said mixture containing about five to forty percent by volume of acetone.

2. A process of removing from oil and gas wells and from petroleum pipe lines those hard, black depos ts which include asphaltenes and which are substantially devoid of readily petroleum-soluble materials, comprising: exposing said deposits to the solvent action of a mixture of about by volume of a liquid-sulfurdioxide extract from a petroleum distillate, about 10% by volume of acetone, and about 35 by volume of cresylic acid.

3. A process of removing from oil and gas wells and from petroleum pipe lines deposits which include asphaltenes and wax and which are substantially devoid of readily petroleum-soluble materials, comprising: exposing said deposits to the solvent action of a mixture of about two parts by volume of gasoline and about one part by volume of acetone.

References Cited in the file of this patent UNITED STATES PATENTS 2,204,224 Limerick et al. June 11, 1940 2,478,456 Boudreaux et a1. Aug. 9, 1949 2,613,186 Pickett et al. Oct. 7, 1952 2,741,596 Luark et al Apr. 10, 1956 OTHER REFERENCES Industrial Solvents, Mellan, 2nd ed., Reinhold Pub. C0., N.Y. (1950), pp. 250-252, 269, 272, 273 and 591. 

1. A PROCESS OF REMMOVING FROM OIL AND GAS WELLS AND FROM PETROLEUM PIPE LINES DEPOSITS WHICH INCLUDE ASPHALTENES AND WHICH ARE SUNBSTANTIALLY DEVOID OF READILY PETROLEUM-SOLUBLE MATERIALS, COMPRISES: EXPOSING SAID DEPOSITS TO THE SOLVENT ACTION OF A MIXTURE INCLUDING A LIQUID-SULFUR-DIOXIDE EXTRACT FROM A PETROLEUM DISTILLATE AND ACETONE, SAID MIXTURE CONTAINING ABOUT FIVE TO FORTY PERCENT BY VOLUME F ACETONE. 